A meticulous accounting of the marathon race to crack the military code the Germans thought was unbreakable.The story begins 10 years before the start of World War II, when the German Embassy demanded the immediate return of a box accidentally mailed to the customs office in Warsaw. Intrigued, Polish intelligence officers dismantled, examined, and reassembled the machine inside before doing so. It was an Enigma machine, a new device for encrypting German military transmissions. Now the Poles had seen the secret machine. A few years later, a German spy sold the French information on how Enigma operated. But the machine could be set in an astronomical number of ways. Alan Turing, a genius British cryptographer working at Bletchley Park, invented the bombe, a machine designed to test the different possibilities. But actually breaking Enigma required code books recovered by British naval officers searching captured German ships-as well as the labor of thousands of enlisted women from the Women's Royal Navy Service who ran the actual bombes. Their grueling cooperative efforts are estimated to have shortened the war by three years. It's an engrossing, complex story, and Barone tells it exceptionally well, with a fluidity and clarity that bely the number of people, not to say countries, involved. Historic photographs illustrate the account, and an epilogue tells what happened to the major players after the war.A riveting true-life adventure story combining brains, courage, and heart. (author's note, map, timeline, bibliography, endnotes) (Nonfiction. 10-16)

Barone (Race to the Bottom of the Earth, rev. 5/21) delivers another impressive feat of narrative nonfiction storytelling. In the years following World War I, Germany developed a virtually unbreakable code, called Enigma, with the help of a complicated machine. One such machine fortuitously fell into the hands of Poland, enabling their ­codebreakers to duplicate the machine and crack the code -- until the Germans added layers of complexity. As Hitler rose to power, the threat of military aggression became obvious, increasing the stakes substantially; the code was central to military operations, particularly the German naval strategy. France, England, and Poland now had extra motivation to cooperate with one another to break the code; and break it they did, but not before an extensive game of ­cat-and-mouse with Germany. ­Accompanied by occasional ­black-and-white ­photos, Barone's suspenseful text introduces a sprawling cast of characters, with the epilogue updating readers on what happened afterward to the central ­players. A timeline, bibliography, and source notes are appended. Jonathan Hunt

A meticulous accounting of the marathon race to crack the military code the Germans thought was unbreakable.The story begins 10 years before the start of World War II, when the German Embassy demanded the immediate return of a box accidentally mailed to the customs office in Warsaw. Intrigued, Polish intelligence officers dismantled, examined, and reassembled the machine inside before doing so. It was an Enigma machine, a new device for encrypting German military transmissions. Now the Poles had seen the secret machine. A few years later, a German spy sold the French information on how Enigma operated. But the machine could be set in an astronomical number of ways. Alan Turing, a genius British cryptographer working at Bletchley Park, invented the bombe, a machine designed to test the different possibilities. But actually breaking Enigma required code books recovered by British naval officers searching captured German ships-as well as the labor of thousands of enlisted women from the Women's Royal Navy Service who ran the actual bombes. Their grueling cooperative efforts are estimated to have shortened the war by three years. It's an engrossing, complex story, and Barone tells it exceptionally well, with a fluidity and clarity that bely the number of people, not to say countries, involved. Historic photographs illustrate the account, and an epilogue tells what happened to the major players after the war.A riveting true-life adventure story combining brains, courage, and heart. (author's note, map, timeline, bibliography, endnotes) (Nonfiction. 10-16)